PROJECT 2 Go wide to grab a planetary system portrait
Zooming out means you can capture not just the planets, but their moons too
When a planet is low in the sky the undulating effects of poor seeing conditions – as the steadiness of the skies are known – can often be exacerbated. This, in turn, makes it more tricky to capture fine details at the high magnifications that are produced by typical high-resolution planetary imaging setups. These employ long focal-length, large aperture scopes and, often, a Barlow lens.
A way to get around this is to not use a Barlow lens, or similar magnifier, when imaging with a high frame-rate camera and this kind of equipment. This will mean you get a wider view of the planet, with its disc appearing smaller in the frame, but the benefit is that the effects of poor seeing will be less obvious. Any unsatisfactory seeing conditions will still degrade the image to a certain extent, but by lowering magnification you also get the advantage of a brighter – albeit smaller – planetary disc. This might mean that you can lower your camera’s gain setting a little, which would have introduced unwanted image noise had it been set high when shooting at a higher magnification.
The biggest perk of a wider shot, though, is that it means you can capture some of the larger moons of Jupiter and Saturn alongside the planet itself. Sometimes, as is often the case with Jupiter’s four Galilean satellites, the moons are bright enough that they show up in a shot that’s been correctly exposed for the planet’s disc. Other times, for example if you’re trying to capture the fainter satellites of Saturn, you may need to capture two video files with your high-frame-rate setup: one exposed for the planet and the other with the exposure length, or gain setting, increased a little to show the dimmer moons. You can composite these two views in image editing software later – after, that is, they have been processed with analysis and stacking software such as RegiStax or AutoStakkert! If you’re creating RGB colour images with a monochrome camera using this last technique, you may wish to simplify the process by capturing the three colour-channel videos required for the planet (red, green, blue) but then only capturing an unfiltered ‘black and white’ video for the faint moons themselves.